International Patent Publication No. WO 2011/116943 describes a moisture sensor for monitoring a vascular access, which is constituted as a textile planar structure of non-conductive warp threads and non-conductive weft threads as well as conductive warp threads and conductive weft threads. The non-conductive warp and weft threads and the conductive warp and weft threads are disposed in the fabric such that an electrically conductive structure with electrical terminals results. The electrical resistance between the terminals is measured in order to detect fluid on moisture. If the fabric is wetted with fluid, the electrical resistance changes so that the fluid is detected.
International Patent Publication No. WO 2010/091852 describes a textile moisture sensor for monitoring a vascular access, wherein the electrically conductive structure with the electrical terminals is printed onto the fabric.
Apart from resistive sensors, capacitive moisture sensors are also known, which comprise an electrically conductive structure made up of a plurality of electrically conductive sections.
The known moisture sensors for monitoring a vascular access, which comprise an electrically conductive structure made up of a plurality of conductive sections, permit monitoring of the functioning capability by the fact that the electrical properties of the sensor are measured under defined conditions and compared with properties preset as a reference value. If the divergences between the measured properties and the properties preset as a reference value exceed or fall below a preset amount, for example, due to a rupture of a strip conductor or a short circuit, it is concluded that there is a faulty moisture sensor.
The known textile moisture sensors are applied on the patient's skin at the puncture point. To monitor a vascular access in an extracorporeal blood treatment, the moisture sensors are stuck, for example, on the patient's forearm. The forearm with a vascular access is generally kept still by the patient during the extracorporeal blood treatment. If, however, the patient moves the forearm during the blood treatment, the moisture sensor is subjected to mechanical stresses, so that the conductive sections of the electrically conductive structure are repeatedly subjected to tensile, compressive or bending stresses. The problem of the mechanical stress arises in the case of textile moisture sensors, wherein warp and weft threads form the electrically conductive structure. There is, however, a risk of rupture of a strip conductor due to micro-cracks also in the case of printed strip conductors.
Textile moisture sensors with woven or printed strip conductors have the advantage that the sensors can be produced cost-effectively in large numbers on a common fabric web. The individual moisture sensors are separated from one another after the weaving and, if necessary, further processing steps.